Crown servants and British council employees
You can still register to vote if you're working outside the UK as a Crown Servant or as an employee of the British Council, or if you're married to, or are the civil partner of, a Crown servant or British Council employee and you're accompanying them during their employment abroad.
Register to vote and check the rules on gov.uk
When you apply, ticking that you want to vote by post or by proxy does not automatically make you one of these types of voters. You will get a separate application form to vote by post or proxy and will remain an elector who votes in person until this form has been completed and returned.
Remember, postal votes can be affected by problems with international post systems and it can't be guaranteed that they will arrive in time. Appointing a proxy is the best way to make sure you're able to cast your vote.